Messages in this thread | | | Date | Thu, 29 Sep 2005 16:52:45 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] vm - swap_prefetch v12 |
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Con Kolivas <kernel@kolivas.org> wrote: > > On Fri, 30 Sep 2005 09:24 am, Andrew Morton wrote: > > Con Kolivas <kernel@kolivas.org> wrote: > > > On Fri, 30 Sep 2005 07:54 am, Andrew Morton wrote: > > > > Con Kolivas <kernel@kolivas.org> wrote: > > > > > Once pages have been added to the swapped list, a timer is started, > > > > > testing for conditions suitable to prefetch swap pages every 5 > > > > > seconds. Suitable conditions are defined as lack of swapping out or > > > > > in any pages, and no watermark tests failing. Significant amounts of > > > > > dirtied ram also prevent prefetching. It then checks that we have > > > > > spare ram looking for at least 3* pages_high free per zone and if it > > > > > succeeds that will prefetch pages from swap. > > > > > > > > Did you consider poking around in gendisk.disk_stats to determine > > > > whether the swap disk(s) are idleish? > > > > > > I didn't know where to look for that info. Thanks! I'm open to *any* > > > suggestions and I'll look into it as I can't take this code much further > > > without outside help. > > > > Might also be able to utilise CFQ's I/O priorities. That should be more > > efective than a heuristic based on disk_stats, however you'd probably need > > to work out whether the swapdev actually supports IO priorities and I'm not > > sure how one would query that (cleanly). > > Good idea. It should be easy to simply add the ioprio value to the kprefetchd > thread and it either supports it or it doesn't depending on what iosched is > being used.
Right. But if the queue doesn't support io priorities then one might want to fall back to monitoring recent queue activity.
> Further to your original suggestion, prefetching is already delayed when any > non-prefetch related swap in or out is occurring already so checking > diskstats is probably not going to add to that for swap activity. However I > assume it (diskstats) could also be used for all disk i/o as well?
Precisely. Few people would set an entire disk aside for swap.
> Currently > a lot of dirty data can tell me that lots of writing is happening but I have > no way of checking that lots of reads are occurring.
diskstats will tell that. Also one could peek at the current disk queue levels (request_list.count[]). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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